关于胸腺瘤描述错误的是（）
A.前纵隔常见肿瘤
B.30%伴有重症肌无力
C.累及心包可出现心包积液
D.好发于青年人
E.以上都不是
参考答案：D
下列关于自由扩散特点的叙述，正确的是[ ]
A．物质从高浓度一边到低浓度一边
B．需要载体协助
C．需要消耗细胞代谢释放的能量
D．物质从低浓度一边到高浓度一边
16. He had already learned the news. I ______ the trouble to phone him about it.
A．needn't have taken
B．could have taken
C．should have taken
D．mustn't have taken
